Methods for depositing nanomaterial, methods for fabricating a device, methods for fabricating an array of devices and compositions

ABSTRACT

A method comprising depositing an ink comprising a nanomaterial, a material capable of transporting charge, and a liquid vehicle from a micro-dispenser onto a layer of a device is disclosed. A method comprising depositing an ink comprising a nanomaterial, a material capable of transporting charge, and a liquid vehicle from a micro-dispenser onto a second material capable of transporting charge in a predetermined arrangement is also disclosed. In certain preferred embodiments, the nanomaterial comprises semiconductor nanocrystals. In certain preferred embodiments, a micro-dispenser comprises an inkjet printhead. Methods for fabricating devices including a nanomaterial and method for fabricating an array of devices including a nanomaterial are also disclosed. An ink composition including a nanomaterial, a material capable of transporting charge, and a liquid vehicle is also disclosed.

This application is a continuation of commonly owned PCT Application No.PCT/US2007/014705 filed 25 Jun. 2007, which was published in the Englishlanguage as PCT Publication No. WO 2008/105792 on 4 Sep. 2008. The PCTApplication claims priority from commonly owned U.S. Patent ApplicationNo. 60/805,736 filed 24 Jun. 2006. The disclosures of each of theabove-listed applications are hereby incorporated herein by reference intheir entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the technical field of nanomaterials,including but not limited to, methods for depositing a nanomaterial,methods for fabricating a device including a nanomaterial, methods forfabricating an array of devices including a nanomaterial, andcompositions including a nanomaterial.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop improvedcompositions and methods for depositing a nanomaterial. It would also beadvantageous to develop improved methods useful for fabricating a deviceincluding a nanomaterial.

In accordance with one aspect of the invention, a method comprisesdepositing an ink comprising a nanomaterial, a material capable oftransporting charge, and a liquid vehicle from a micro-dispenser onto asubstrate. In certain embodiments, the substrate further includes alayer of a device disposed over the substrate. In these embodiments, thelayer of a device comprises a material and the ink is deposited onto thelayer.

In certain embodiments, the ink is deposited onto a layer of a devicedisposed onto a substrate. In certain embodiments, the substrate furtherincludes a layer of a device disposed over the substrate. In theseembodiments, the layer of a device comprises a material and the ink isdeposited onto the layer.

In certain embodiments, the ink is deposited in a predeterminedarrangement. For example, the ink can be deposited in a patterned orunpatterned arrangement.

In certain embodiments, the nanomaterial comprises inorganicnanoparticles capable of emitting light.

In certain embodiments, the nanomaterial comprises semiconductornanocrystals. Semiconductor nanocrystals possess characteristics andproperties that make them particularly well-suited for use in a varietyof devices and other end-use applications, including, but not limitedto, light emitting devices, displays, photodetectors, nonvolatile randommemory devices, solar cells, sensors, photovoltaic devices, etc.

In certain embodiments, the nanomaterial comprises semiconductornanocrystals wherein at least a portion of the semiconductornanocrystals include one or more ligands attached to a surface thereof.

In certain embodiments, the method comprises depositing an inkcomprising a nanomaterial comprising semiconductor nanocrystals, amaterial capable of transporting charge, and a liquid vehicle from amicro-dispenser onto a layer of a device. The layer of the devicecomprises a material.

In certain embodiments, the ink is deposited in a predeterminedarrangement. For example, the ink can be deposited in a patterned orunpatterned arrangement.

In certain embodiments, the method further comprises removal of theliquid vehicle from the ink. In certain embodiments, the liquid vehicleis selected such that, upon removal of the liquid vehicle, the layerincluding the nanomaterial deposited thereon is planar.

In certain embodiments, the liquid vehicle comprises a liquid in whichthe material included in the layer onto which the ink is deposited isinsoluble.

In certain embodiments, the liquid vehicle comprises a liquid in whichthe material included in the layer onto which the ink is deposited is atleast partially soluble.

In certain embodiments, the material included in the layer onto whichthe ink is deposited is sufficiently soluble in the liquid such that atleast a portion of the nanomaterial can become at least temporarilymixed in the portion of the material of the layer that dissolves in theliquid. In certain embodiments, the liquid can be removed such that atleast a portion of the material of the layer and the nanomaterial remainmixed. In certain embodiments, the liquid can be removed such that thenanomaterial phase separates to form a layer of nanomaterial at or nearthe surface of the layer.

In certain embodiments, the material included in the layer onto whichthe ink is deposited is sufficiently soluble in the liquid such that atleast a portion of the nanomaterial and the material capable oftransporting charge that are included in the ink can become at leasttemporarily mixed in the portion of the material of the layer thatdissolves in the liquid. In certain embodiments, the liquid can beremoved such that at least a portion of the material of the layer andthe nanomaterial and the material capable of transporting charge remainmixed.

In certain embodiments, the liquid can be removed such that thenanomaterial phase separates to form a layer of nanomaterial at or nearthe surface of the layer.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises a second material capable of transporting charge.The second material capable of transporting charge onto which the ink isdeposited can be the same as or different from the material capable ortransporting charge that is included in the ink.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises a small molecule material. A “small molecule”material refers to any organic material that is not a polymer. A smallmolecule material can further include a metal. A small molecule caninclude an organometallic compound. A small molecule material caninclude a metal complex. A small molecule material can include repeatingunits in some circumstances. For example, using a long chain alkyl groupas a substituent does not remove a molecule from the “small molecule”class. Other examples of small molecule materials can include organicoligomer molecules (e.g., organic molecules of intermediate relativemolecular mass, the structure of which essentially comprises a smallplurality of units derived, actually or conceptually, from molecules oflower relative molecular mass, see “oligomer molecule” from IUPACCompendium of Chemical Terminology 2^(nd) Edition (1997) includingrelated Notes, which are hereby incorporated herein by reference.)

In certain embodiments, a small molecule material may serve as the coremoiety of a dendrimer, which includes a series of chemical shells builton the core moiety. The core moiety of a dendrimer may be a fluorescentor phosphorescent small molecule emitter.

Dendrimer substituents can also be used to enhance the ability of smallmolecules to undergo solution processing.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises a polymer.

In certain embodiments, the layer of the device onto which the ink isdeposited can comprise an organic nanocrystal. Examples of organicnanocrystals include, without limitation, J-aggregates, H-aggregates,and organic nanocrystals including aggregates with other dipolearrangements. Examples of organic nanocrystals are described in S.Kirstein et al., “Herringbone Structures In Two-Dimensional SingleCrystals of Cyanine Dyes. I. Detailed Structure Analysis Using ElectronDiffraction”, J. Chem. Phys. 103(2) July 1995, pages 816 et seq.; S.Kirstein et al., “Herringbone Structures In Two-Dimensional SingleCrystals of Cyanine Dyes. II. Optical Properties”, J. Chem. Phys. 103(2)July 1995, pages 826 et seq.; A. Mishra et al. “Cyanines During the1990s: A Review”, Chem. Rev. 2000, 100, 1973-2011; and C. Peyratout etal., “Aggregation of Thiacyanine Derivatives On Polyelectrolytes:, Phys.Chem. Chem. Phys., 2002, 4, 3032-3039, the disclosures of which arehereby incorporated herein by reference in their entireties.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises carbon nanotubes.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises a carbon nanotube/polymer blend or hybrid.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises an inorganic material.

In certain embodiments, the layer of the device onto which the ink isdeposited can be disposed over a substrate which may also include anelectrode.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises an electrode.

In certain embodiments, one or more other layers can be disposed overthe substrate before the ink.

In certain embodiments, the method can further include depositing asecond electrode layer over the nanomaterial. The deposition of one ormore additional layers (including, for example, hole blocking layer,electron transport layer, electron injection layer, etc.) can alsooptionally be included before or after deposition of the secondelectrode layer. Passivation, packaging, etc. can also optionally beincluded.

In accordance with another aspect of the invention, a method comprisesdepositing an ink comprising a nanomaterial, a material capable oftransporting charge, and a liquid vehicle from a micro-dispenser onto asecond material capable of transporting charge.

In certain embodiments, the ink is deposited in a predeterminedarrangement. For example, the ink can be deposited in a patterned orunpatterned arrangement.

The material capable of transporting charge included in the ink can bethe same as or different from the second material capable oftransporting charge onto which the ink is deposited. In certainembodiments, the material capable of transporting charge included in theink can be at least partially soluble in the liquid vehicle.

In certain embodiments of the invention, the nanomaterial comprisesinorganic nanoparticles capable of emitting light.

In certain embodiments of the invention, the nanomaterial comprisessemiconductor nanocrystals. Semiconductor nanocrystals possesscharacteristics and properties that make them particularly well-suitedfor use in a variety of devices and other end-use applications,including, but not limited to, light emitting devices, displays,photodetectors, nonvolatile random memory devices, solar cells, sensors,photovoltaic devices, etc.

In certain embodiments, the nanomaterial comprises semiconductornanocrystals wherein at least a portion of the semiconductornanocrystals include one or more ligands attached to a surface thereof.

In certain embodiments, the ink is deposited in a predeterminedarrangement. For example, the ink can be deposited in a patterned orunpatterned arrangement.

In certain embodiments, the method further comprises removal of theliquid vehicle from the ink. In certain more detailed embodiments, theliquid vehicle is selected such that, upon removal of the liquidvehicle, the surface of the second material capable of transportingcharge onto which the nanomaterial is deposited is planar.

In certain embodiments, the liquid vehicle comprises a liquid in whichthe second material capable of transporting charge is insoluble.

In certain embodiments, the liquid vehicle comprises a liquid in whichthe second material capable of transporting charge is at least partiallysoluble.

In certain embodiments, the second material of transporting charge issufficiently soluble in the liquid such that at least a portion of thenanomaterial can become at least temporarily mixed in the portion of thesecond material capable of transporting charge that dissolves in theliquid. In certain more detailed embodiments, the liquid can be removedsuch that at least a portion of the second material capable oftransporting charge and the nanomaterial remain mixed. In certainembodiments, the liquid can be removed such that the nanomaterial phaseseparates to form a layer of nanomaterial at or near the surface of thesecond material capable of transporting charge.

In certain embodiments, the second material of transporting charge issufficiently soluble in the liquid such that at least a portion of thenanomaterial and material capable of transporting charge can become atleast temporarily mixed in the portion of the second material capable oftransporting charge that dissolves in the liquid. In certain moredetailed embodiments, the liquid can be removed such that at least aportion of the second material capable of transporting charge, thenanomaterial, and the material capable of transporting charge remainmixed. In certain embodiments, the liquid can be removed such that thenanomaterial phase separates to form a layer of nanomaterial at or nearthe surface of the second material capable of transporting charge.

In accordance with another aspect of the invention there is provided amethod of fabricating a device. The method comprises depositing an inkincluding a nanomaterial comprising semiconductor nanocrystals, amaterial capable of transporting charge, and a liquid vehicle from amicro-dispenser over a substrate including an electrode. The substratemay optionally include one or more additional layers and/or features. Inanother detailed aspect, following deposition onto the substrate, theliquid vehicle is removed from the ink. In another detailed aspect, oneor more additional layers and/or features are disposed over thesemiconductor nanocrystals.

In accordance with another aspect of the invention, there is provided amethod for forming an array of devices comprising: depositing an inkcomprising a nanomaterial comprising semiconductor nanocrystals, amaterial capable of transporting charge, and a liquid vehicle from amicro-dispenser in a predetermined arrangement over a substrateincluding an electrode. For example, the ink can be deposited in apatterned or unpatterned arrangement.

The substrate may optionally include one or more additional layersand/or features. In another detailed aspect, following deposition ontothe substrate, the liquid vehicle is removed from the ink. In anotherdetailed aspect, one or more additional layers and/or features aredisposed over the semiconductor nanocrystals. In certain embodiments twoor more inks including different light-emissive materials are depositedin a predetermined arrangement. For example, the ink can be deposited ina patterned or unpatterned arrangement.

In accordance with another aspect of the invention, there is provided anink composition comprising a nanomaterial, a material capable oftransporting charge, and a liquid vehicle. In certain embodiments, theink composition comprises a dispersion. For certain applications, it isdesirable for the dispersion to be colloidal.

In certain embodiments, the nanomaterial comprises semiconductornanocrystals.

In certain embodiments, the ink composition comprises a nanomaterialcomprising semiconductor nanocrystals, a material capable oftransporting charge, and a liquid vehicle, wherein the material capableof transporting charge has a triplet energy which is at least greaterthan the bandgap of the semiconductor nanocrystals included in the ink.

In certain aspects and embodiments of the present invention, the liquidvehicle comprises a composition including one or more functional groupsthat are capable of being cross-linked by UV or thermal treatment oranother cross-linking technique readily ascertainable by a person ofordinary skill in a relevant art.

The foregoing, and other aspects described herein all constituteembodiments of the present invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed. Other embodimentswill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 depicts a schematic of an example of an equipment set-up for usein carrying out an embodiment of a method in accordance with theinvention.

FIG. 2 depicts a schematic of an example of a structure of alight-emitting device.

FIG. 3 depicts a schematic of an example of a structure of alight-emitting device.

The attached figures are simplified representations presented forpurposed of illustration only; the actual structures may differ innumerous respects, including, e.g., relative scale, etc.

For a better understanding to the present invention, together with otheradvantages and capabilities thereof, reference is made to the followingdisclosure and appended claims in connection with the above-describeddrawings.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with one aspect of the invention, a method comprisesdepositing an ink comprising a nanomaterial, a material capable oftransporting charge, and a liquid vehicle from a micro-dispenser onto asubstrate. In certain embodiments, the substrate further includes alayer of a device disposed thereover. In these embodiments, the layer ofa device comprises a material and the ink is deposited onto the layer ofa device. In accordance with another aspect of the invention, a methodcomprises depositing an ink comprising a nanomaterial comprisingsemiconductor nanocrystals, a material capable of transporting charge,and a liquid vehicle from a micro-dispenser onto a substrate. In certainembodiments, the substrate further includes a layer of a device disposedthereover. In these embodiments, the layer of a device comprises amaterial and the ink is deposited onto the layer of a device.

It is believed that the present invention can offer significantadvantages, especially, for example, for devices including largesubstrates, e.g., larger than about 0.5 meters in at least one dimensionand/or when predetermined arrangements of nanomaterial are desired.

In accordance with another aspect of the invention, a method comprisesdepositing an ink comprising a nanomaterial, a material capable oftransporting charge, and a liquid vehicle from a micro-dispenser onto asecond material capable of transporting charge in a predeterminedarrangement. For example, the ink can be deposited in a patterned orunpatterned arrangement. In certain embodiment, the ink is depositedonto a layer comprising the second material capable of transportingcharge.

The material capable of transporting charge included in the ink can bethe same as or different from the second material capable oftransporting charge onto which the ink is deposited. In certainembodiments, the material capable of transporting charge included in theink is at least partially soluble in the liquid vehicle.

In certain embodiments, the ink can be deposited from a micro-dispenser,such as an inkjet printhead of an inkjet printing system. Inkjetprinting can allow a pattern of ink including a nanomaterial andmaterial capable of transporting charge to be conveniently formed on alayer of a device. Inkjet printing can allow precise control over thelocation and size of inked areas that are printed. Ink spots of about 20μm in size are readily achievable today by commercially available inkjetprinters, and smaller spot sizes are expected to be possible. Differentnanomaterials can be patterned simultaneously using an inkjet printingsystem having multiple print heads. Thus, multiple nanomaterials can bedeposited in a single deposition step. This avoids the need to registersubsequent depositions to a previously deposited pattern.

An inkjet printing system for use in depositing a nanomaterial and amaterial capable of transporting charge can include a printhead having afiring chamber reservoir containing an ink. In one embodiment, an inkjetprinting system, for example, can be used to propel the ink onto thematerial or device layer to be printed using resistive heating elementsor piezoelectric elements for propelling the composition through anoverlying orifice plate. The ink can be stored in a reservoir and thecomposition can travel through a set of micro-channels toward theorifice plate. The printhead can have a firing chamber reservoircontaining the ink.

Examples of inkjet printing systems for use in carrying out the methodsof the invention include, without limitation, Dimatix Materials PrinterDMP-2800 Series including Dimatix Materials Cartridge DMC-1000 Series,of Dimatix, Inc., Santa Clara, Calif. Inkjet printing systems from othermanufacturers may also be useful in carrying out the methods of theinvention. See also inkjet printing systems described in U.S. Pat. No.6,997,539 for “Apparatus for Depositing Droplets” of Hoisington et al.(assigned to Dimatix, Inc.), issued on 14 Feb. 2006; U.S. Pat. No.7,011,936 for “Piezoelectric Ink Jet Module With Seal” of Moynihan etal. (assigned to Dimatix, Inc.), issued on 14 Mar. 2006. The foregoingpatents are hereby incorporated herein by reference in their entirety.Examples of other inkjet printing systems include the Omnidot printeravailable from the Xaar Corporation headquartered in Cambridge, UK.Another example of a nozzle array is a multi-jet nozzle system thatincludes 126 jets and is sold under the part number XJ126 by XaarCorporation. Furthermore, an atomization spray process using anultrasonic spray head to dispense ink droplets may be employed.Additionally, for inks with high viscosities, e.g., 20 centipoise orgreater, the Leopard available from the Xaar Corporation may beemployed, wherein the ink may be heated to reduce the viscosity to ajettable range.

An example of another inkjet system which is more suitable to researchand development needs is the Active Pipette™ piezo system available fromEngineering Arts.

An inkjet printing system can include, for example, a data interface, acontrol subsystem, a positioning subsystem, and a depositing subsystem.It should be appreciated that in other embodiments of the invention, anink including a nanomaterial comprising semiconductor nanocrystals, amaterial capable of transporting charge, and a liquid vehicle may bedeposited onto a substrate, a material or device layer by any of avariety of other delivery systems including one or moremicro-dispensers, including but not limited to thermal ejection,piezoelectric ejection, aerosol generation, micropipettes, pipettes,ultrasonic printheads, etc. that can be configured to dispense aselected volume of solution with the desired application parameters.

Current inkjet technology allows for orifice sizes of from about 15 μmto about 100 μm. Thus, the minimum size of the features that can bedeposited is currently limited to about this range, although futuredevelopments may allow for smaller orifice sizes and decreased sizes.Additionally, the size of the orifice can affect the practical size ofany nanomaterial present in the ink to be inkjetted.

In certain embodiments, inkjetting techniques can include an inkformulation which is tailored to various inkjet pens, including thermal,piezoelectric, sonic impulse, or other known inkjet printing systems. Asdiscussed above, an ink can further include a variety of components suchas those typically used in inkjet liquid vehicles, such as, but notlimited to solvents, cosolvents, surfactants, biocides, buffers,viscosity modifiers, sequestering agents, colorants, stabilizing agents,humectants, scatterers, fillers, extenders, water, and mixtures thereof.Several considerations in selecting the amount of liquid vehicle includethose related to nucleation such as heat capacity, heat of vaporization,critical nucleation temperature, diffusivity, and the like. Typically,an ink for use in thermal inkjet printing systems can have a viscosityof from about 0.8 cP to about 20 cP, and in some cases, can be up to 50cP. Similarly, an ink for use in piezoelectric inkjet printing systemscan have a viscosity of from about 2 cP to about 15 cP, and in somecases, can be up to 30 cP. Optionally, a viscosity modifier can beincluded in the ink. Examples of viscosity modifiers include2-pyrrolidone, isopropyl alcohol, glycerol, and the like. However, otherviscosity modifiers can be used.

The surface tension of an ink used in thermal inkjet printing systemscan range from about 25 dyne/cm to about 75 dyne/cm, and in someembodiments, can be from about 30 to about 55 dyne/cm. The surfacetension can be adjusted using compounds such as isopropyl alcohol,ethanol, methanol, glycerol, and the like. In certain embodiments, theliquid vehicle can include from about 60 wt % to about 100 wt % of theink. Various techniques can be used to modify the viscosity or otherjetting properties of the ink. For example, heat can be used to liquefymaterial, increase solubility of the material, or reduce viscosity suchthat it becomes inkjettable. Those skilled in the art will recognizethat the above discussion is primarily focused on thermal inkjetprinting systems; piezoelectric inkjet printing systems involve lessrestrictive considerations. For example, thermal inkjet printing systemsare typically operated at temperatures below about 80° C., whilepiezoelectric inkjet printing systems can be operated at temperatures ofup to about 150° C. Those skilled in the art will recognize whichcomponents can be included in the liquid vehicle in order to inkjet anink from thermal, piezoelectric, or other inkjet printing systems. Thoseskilled in the art can adjust these and other variables to achieve avariety of resolutions and conductive paths. Printhead waveforms (e.g.,piezo and thermal excitation waveforms, anti-clogging waveforms,ejection waveforms, etc.), and the compositions of the materials used toconstruct the printhead and orifice plate are among such variables. Forexample, depending on the wetting attributes of the ink and thewettability of the internal surface of the inkjet nozzle or the surfaceof the printing orifice plate, the ink composition can be treated toenhance drop ejection.

In certain embodiments of the inventions described herein, it may bebeneficial to use a vehicle system which would result in ink propertiesfalling outside the normal ranges described above. This would be thecase, for example, if one were to use a vehicle in which the material ofthe device is insoluble. An example of a class of solvents that meetthis criterion are fluorinated solvents, such as perfluorodecalin, orthe Fluorinert series of solvents sold by 3M. In creating inks from suchsolvents, the surface tension and viscosity may fall below thosenormally required for inkjet. Fluorinert FC-77, for example, has asurface tension of 13 dyne/cm and a viscosity of 1.3 cP. A method tomore consistently jet inks made with these solvents includes creating anegative pressure (relative to atmospheric) inside the cartridgereservoir to form a jet that is more stable. This can be accomplished atlaboratory scale by placing the cartridge reservoir slightly below theinkjet nozzle. The positioning of the cartridge reservoir to achieve asufficient negative pressure therein to form a jet can be readilydetermined by one of ordinary skill in the art. Preferably, the inkjetcartridge reservoir is held by or positioned relative to the inkjetnozzle(s) such that the height of inkjet cartridge reservoir can beadjusted to obtain the desired negative pressure inside the cartridgereservoir. In one example, the cartridge reservoir is positioned on avariable-height platform (e.g., a small jack), the height of which canbe adjusted to obtain a negative pressure inside the cartridgereservoir, preferably a slight negative pressure. A schematic diagram ofan example of a laboratory-scale set-up is shown in FIG. 1. In certainembodiments, semiconductor nanocrystals included in a fluorinatedsolvent include one or more fluorinated ligands attached to a surface ofthe nanocrystals. Nanocrystals including fluorinated ligands can beprepared by exchanging at least one or more ligands that become attachedto a nanocrystal surface during, e.g., colloidal synthesis, with ligandsthat include a functional head such as, by way of example, a thiol,carbodithioate, carbodithioic acid, amine, thiourea, amide, phosphineoxide, phosphonic or phosphinic acid, thiophosphonic or thiophosphinicacid, which functional head can be substituted with alkyl and/or arylunits that are perfluorinated or partially fluorinated. Preferably thefluorinated ligand is chemically compatible with the fluorinated liquidvehicle.

Deposition of nanomaterial onto the surface to be printed in the form ofejected drops produces a “dot” of ink comprising a nanomaterial, amaterial capable of transporting change, and liquid vehicle thereon. Theterm “dot” is used to refer to the ink drop once it contacts thesurface. In some examples, the ink in the drop will stay in a thin layeron the surface. However, depending on the porosity, wettability, and/oror other attributes of the device layer, and when the drop contacts thelayer, the ink can spread outwardly resulting in dot gain. Dot gain isthe ratio of the final diameter of a dot on the surface to its initialdiameter. If the material or layer onto which the ink is deposited isporous, the dot can penetrate into the material or layer. Dotpenetration is the depth that the drop soaks into the surface on whichit is deposited. The physical and/or chemical properties of the dots canenhance dissolution rates without disrupting the permeability andspecificity of the ink. Controlled dot placement, high surface-to-massratio of the dots, and digital mass deposition control of the dots canbe used to address performance of the deposited nanomaterial andmaterial capable of transporting charge in the device.

For example, a dot has virtually no dot gain or dot penetration, as maybe the case, when an ejection solution is applied to a deliverysubstrate having a nonwettable, surface, or a relatively impermeablesurface.

One convenient way of quantifying the nature of the interaction betweenthe ink forming the dot and the surface onto which it is deposited, isto measure the angle θ formed by the liquid-solid and the liquid-airinterfaces. This angle, referred to as the contact angle, is a productof the surface tension of the solution as well as the wettability of thesurface onto which the ink is deposited. Inks including a liquid vehiclehaving a high surface tension, and poor interaction with the surface ofthe device layer to be printed tend to exhibit contact angles greaterthan 90°. The ink then tends to form discrete droplets on the surface.However, where the liquid vehicle is relatively nonpolar, as istypically the case with an organic liquid, and the surface onto whichthe ink is deposited device layer is similarly nonpolar, the contactangle is typically less than 90°, and the liquid tends to spread out andform a thin film. As the dot spreads out and thins, the contact angletends to zero.

As described above, an inkjet printing system may be adapted to depositone or more different inks comprising nanomaterials comprising differentsemiconductor nanocrystals and a material capable of transportingcharge, which may be included in corresponding inks. The materialcapable of transporting charge that is included in each ink can be thesame or different. In certain embodiments, the same material capable oftransporting charge is included in each of the inks being deposited. Insome embodiments, two or more ejection cartridges can be configures foreach to deposit an ink including a different nanomaterial and/or ejectink having different drop volumes. The inkjet system may be configuredto interchangeably receive different ejection cartridges, which areindividually configured to apply the same of different ink to thesurface being printed. Interchangeable ejection cartridges may also beused to replace an empty ejection cartridge with a full ejectioncartridge. It is within the scope of this disclosure to utilize othermechanisms for depositing an ink including a nanomaterial, a materialcapable of transporting charge, and a liquid vehicle onto a material orlayer of a device, and ejection cartridge is provided as a nonlimitingexample. For example, an inkjet system may include an ejection cartridgethat utilizes an ejection-head having ejectors configured to effectuatefluid ejection via a nonthermal mechanism, such as vibrationaldisplacement caused by a piezoelectric ejection element.

In one example of an inkjet system that may be useful in carrying outmethods in accordance with the invention, the nozzle spacing can beabout 504 μm, the nozzle diameter can be about 27 μm; and the dropletsize (for 12 pl) spreads to minimum size ˜5 μm square.

Based on estimated nozzle life, a nozzle can be expected to coat an areaof about 807 ft2. This area corresponds to printing 29,000 two-inchsquares or 3,200 six inch square displays. The range of fluidviscosities that can be inkjet printed includes, for example, 8-14 cP.Printing at operating temperatures over 70° C. may be limited by thespecific materials and equipment used.

Depending upon the drop volume, contact angle, viscosity, and otherproperties of the ink, even with a drop volume as small as ˜8 pl, thespot diameter can be relatively large due to rapid spreading. Similarly,depending upon the drop volume, contact angle, and viscosity, and otherproperties of the ink, in some instances, to print a linear pattern froman inkjet printing system, repeat printing of drops in an overlappingarrangement may be appropriate.

As discussed above, an ink useful for depositing nanomaterial from amicro-dispenser includes nanomaterial and a liquid vehicle. In certainembodiments, the liquid vehicle comprises a liquid in which thenanomaterial can be dispersed or suspended. In certain preferredembodiments, the nanomaterial is colloidally dispersed. In certainembodiments, the liquid vehicle comprises a liquid in which thenanomaterial does not dissolve or does not appreciably dissolve (e.g.,solubility is less than 0.001 mg/ml).

In certain embodiments including a nanomaterial including one or moreligands attached to a surface of at least a portion of the nanoparticlesthereof, the liquid vehicle comprises a liquid in which suchnanomaterial with attached ligands can be dispersed or suspended. Incertain preferred embodiments, the nanomaterial is colloidallydispersed. In certain embodiments, the nanoparticles comprisesemiconductor nanocrystals. In certain embodiments, the liquid vehicleis one in which the ligands (when not attached to nanoparticles) are atleast partially soluble. In certain embodiments, the liquid vehicle isone in which the ligands (when not attached to nanoparticles) areinsoluble.

In certain embodiments, the ink includes a liquid vehicle in which thematerial or device layer onto which the ink is to be deposited isinsoluble (e.g., <0.001/mg/ml of the material dissolves in the liquidvehicle). In other certain embodiments, the ink includes a liquidvehicle in which the material or device layer onto which the ink is tobe deposited is at least partially soluble (e.g., >0.001 mg/ml of thematerial dissolves in the liquid vehicle). In certain embodiments, atleast a portion of the nanomaterial can become at least temporarilymixed in the portion of the material or layer that dissolves in the ink.In certain embodiments, at least a portion of the nanomaterial andmaterial capable of transporting charge can become at least temporarilymixed in the portion of the material or layer that dissolves in the ink.

In certain embodiments, the method further comprises removal of theliquid vehicle from the ink.

In certain embodiments, the liquid vehicle can be removed such that atleast a portion of the material or layer and the nanomaterial remainmixed. In certain embodiments, the liquid vehicle can be removed suchthat at least a portion of the material or layer, the nanomaterial, andthe material capable of transporting charge remain mixed.

In another embodiment, the liquid vehicle can be removed such that thenanomaterial phase separates to form a layer of nanomaterial at or nearthe surface of the underlying material or layer. Phase separation isdescribed in more detail in U.S. patent application Ser. No. 10/400,907for “Layered Materials Including Nanoparticles” of Bulovic et al. filedon 28 Mar. 2003, which is hereby incorporated herein by reference in itsentirety.

In certain embodiments, the liquid vehicle of the ink is selected suchthat, upon removal of the liquid vehicle, the material or layer(s) ofthe device including the nanomaterial deposited thereon is planar. Anexample of a technique for achieving a planer material or device layerinvolves utilizing a well structure such as typically used in PLEDtechnology. Other techniques can be readily determined by one ofordinary skill in the relevant art. One technique for measuringplanarity is by measuring peak-to-peak height difference. This can bereadily measured using an AFM microscope. In certain embodiments, aplanar layer has a peak-to-peak height difference less than about 5%.

Examples of a liquid vehicle for inclusion in an ink including ananomaterial (e.g., a nanomaterial comprising semiconductornanocrystals) and a material capable of transporting charge include,without limitation, those listed in the following Table 1, and mixturesof two or more thereof.

Examples of mixtures include, but are not limited to, hexane and octane;benzene and xylene; tetrahydrofurane and anisole; etc.

TABLE 1 Relative Boiling Polarity Viscosity Point (compared LiquidFormula @25° C. @1 atm to water) cyclohexane C₆H₁₂ 0.89 80.7 0.006pentane C₅H₁₂ 0.24 36.1 0.009 hexane C₆H₁₄ 0.30 69 0.009 heptane C₇H₁₆0.91 98 0.012 carbon tetrachloride CCl₄ 0.91 76.7 0.052 p-xylene C₈H₁₀0.63 138.3 0.074 toluene C₇H₈ 0.56 110.6 0.099 benzene C₆H₆ 0.60 80.10.111 diethyl ether C₄H₁₀O 0.22 34.6 0.117 methyl t-butyl C₅H₁₂O 55.20.148 alcohol dioxane C₄H₈O₂ 1.21 101.1 0.164 tetrahydrofurane C₄H₈O0.47 66 0.207 (THF) ethyl acetate C₄H₈O₂ 77 0.228 dimethoxy-ethaneC₄H₁₀O₂ 85 0.231 (glyme) diglyme C₆H₁₄O₃ 162 0.244 chloroform CHCl₃ 0.5461.2 0.259 methylene chloride CH₂Cl₂ 0.43 39.8 0.309 2-butanone C₄H₈O79.6 0.327 acetone C₃H₆O 0.31 56.2 0.355 t-butyl alcohol C₄H₁₀O 82.20.389 dimethyl- C₃H₇NO 153 0.404 formamide (DMF) dimethyl sulfoxideC₂H₆OS 189 0.444 (DMSO) acetonitrile C₂H₃N 0.35 81.6 0.46 2-propanolC₃H₈O 2.40 82.4 0.546 1-butanol C₄H₁₀O 3.00 117.6 0.602 1-propanol C₃H₈O1.95 97 0.617 acetic acid C₂H₄O₂ 118 0.648 ethanol C₂H₆O 1.20 78.5 0.654diethylene glycol C₄H₁₀O₃ 35.70 245 0.713 methanol CH₄O 0.59 64.6 0.762ethylene glycol C₂H₆O₂ 16.90 197 0.79 glycerin C₃H₈O₃ 1410.00 290 0.812water, heavy (D2O) D₂O 101.3 0.991 water H₂O 1.00 100 1 Nonane(CH₃(CH₂)₇CH₃) 0.67 39.0 Decane C₁₀H₂₂ 0.84 174.1 Dodecane C₁₂H₂₆ 1.25216.2 Chlorobenzene C₆H₅Cl 0.75 132 Dichlorobenzene C₆H₄Cl₂ _(—) 174.0Anisole C₇H₈O 0.92 154.0 Dimethyl HCON(CH₃)₂ 0.79 149.56 formamide1-Methyl-2- 1.7 204.5 pyrrolidinone Carbon tetrachloride CCl₄ 0.91 76.81,1,1-Trichloro- CH₃CCl₃ 0.73 74.0 ethane Tetrachloroethylene ClCH═CCl₂0.57 87.0 Ethylbenzene C₈H₁₀ 0.67 136.0 Fluorinert FC-77 (a 1.3 97.0 3Mproduct)

Other liquids or mixtures of liquids can be used as a liquid vehicle. Incertain embodiments, volatile liquids or mixtures of volatile liquidscan be used as a liquid vehicle.

In certain embodiments, an ink including a nanomaterial, a materialcapable of transporting charge, and a liquid vehicle has a viscosity ina range of from about 0.1 centipoise (e.g., that of diethyl ether,methanol) to greater than 1500 centipoise (e.g., that of oils,glycerol).

Examples of a material capable of transporting charge that can beincluded in the ink include any material that can be used in a holetransport layer, an electron transport layer, a hole injection layer, oran electron injection layer, which are described elsewhere herein.

In certain embodiments, the ink includes a material capable oftransporting charge having a triplet energy which is at least greaterthan the bandgap of the semiconductor nanocrystals included in the ink.

The amount (e.g., concentration (wt/vol)) of material capable oftransporting charge included in an ink can be selected based upon theparticular material, nanomaterial and desired attributes of thedeposited nanomaterial and material capable of transporting charge(e.g., thickness, optical density, features of the depositednanomaterial (e.g., patterned or unpatterned, sizes of the features of apattern, etc.)). The amount can be readily determined by a person ofordinary skill in the art.

For example, a material capable of transporting charge can be includedin the ink in an amount of, for example, about 0.1 mg/ml to about 50mg/ml; about 1 mg/ml to about 20 mg/ml; about 5 mg/ml to about 15 mg/ml.

In certain embodiments, the material capable of transporting chargeincluded in the ink is at least partially soluble in the liquid vehicle.In certain embodiments including a nanomaterial comprising semiconductornanocrystals at least a portion of which have one or more ligandsattached to a surface thereof, the ligands and material capable oftransporting charge can be chemically similar such that they do notreadily separate in the liquid vehicle due to chemical dissimilarities.In certain embodiments including a nanomaterial comprising semiconductornanocrystals including one or more ligands attached to a surface of atleast a portion of the semiconductor nanocrystals, the ligands andmaterial capable of transporting charge can be chemically dissimilarsuch that they separate into layers or phases in the liquid vehicle dueto chemical dissimilarities.

In certain embodiments including a nanomaterial comprising semiconductornanocrystals, the liquid vehicle comprises an organic non-polar liquid.In certain embodiments, the liquid vehicle has a viscosity less than orequal to about 1 cP and also relatively high volatility.

In certain embodiments of the inventions described herein, it is notnecessary to have the nanomaterial particles (e.g., semiconductornanocrystals) individually dispersed in the vehicle. The nanomaterialparticles (e.g., semiconductor nanocrystals may be aggregated. Incertain embodiments of the inventions described herein, the nanomaterialparticles (e.g., semiconductor nanocrystals) may be included within oradsorbed onto polymer particles. In certain embodiments of theinventions described herein, the nanomaterial particles (e.g.,semiconductor nanocrystals) may be included within or adsorbed onto amatrix. The matrix can be polymeric or non-polymeric.

Optionally, other components can be included in the ink. Examples ofother components that can be optionally included in the ink include, butare not limited to, e.g., surfactants, solvents, co-solvents, buffers,biocides, viscosity modifiers, complexing agents, chelating agents,stabilizing agents (e.g., to inhibit agglomeration of the nanomaterial),humectants, scatterers, fillers, extenders etc. Other possiblecomponents include other additives of the type that may be included inink or inkjet ink compositions. Stabilizing agents can include, e.g.,chemically attached functional groups or ligands to form a coatingaround individual nanoparticles.

The amount (e.g., concentration (wt/vol)) of nanomaterial included in anink can be selected based upon the particular nanomaterial and desiredattributes of the deposited nanomaterial (e.g., thickness, opticaldensity, features of the deposited nanomaterial (e.g., patterned orunpatterned, sizes of the features of a pattern, etc.)). The amount canbe readily determined by a person of ordinary skill in the art.

For example, in certain embodiments of inks including a nanomaterialcomprising semiconductor nanocrystals, a material capable oftransporting charge, and a liquid vehicle (including, e.g., but notlimited to, a liquid vehicle comprising non-polar organic liquid orliquid mixture), the ink can include at least about 0.1 mg/mlsemiconductor nanocrystals. In examples of other embodiments, the inkcan include at least 1 mg/ml, at least 5 mg/ml, at least 10 mg/ml, atleast 25 mg/ml; at least 50 mg/ml, etc.

In certain embodiments, the nanomaterial, material capable oftransporting charge, and any other optional components are dispersed inthe ink when deposited. In certain preferred embodiments, the dispersionis colloidal.

A nanomaterial includes nanoparticles having an average maximumdimension smaller than 100 nm.

In certain preferred embodiments, the nanomaterial comprisessemiconductor nanocrystals.

Semiconductor nanocrystals comprise nanometer-scale inorganicsemiconductor particles. Semiconductor nanocrystals preferably have anaverage nanocrystal diameter less than about 150 Angstroms (Å), and mostpreferably in the range of 12-150 Å.

Semiconductor nanocrystals include, for example, inorganic crystallitesbetween about 1 nm and about 1000 nm in diameter, preferably betweenabout 2 nm and about 50 nm, more preferably about 5 nm to about 20 nm(such as about 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20nm).

The semiconductor forming the semiconductor nanocrystals can comprise aGroup IV element, a Group II-VI compound, a Group II-V compound, a GroupIII-VI compound, a Group III-V compound, a Group IV-VI compound, a GroupI-III-VI compound, a Group II-IV-VI compound, a Group II-IV-V compound,alloys of any of the foregoing, and/or mixtures of any of the foregoing,including ternary and quarternary mixtures and/or alloys. Examplesinclude, but are not limited to, ZnO, ZnS, ZnSe, ZnTe, MgO, MgS, MgSe,MgTe, CdO, CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb,GaN, GaP, GaAs, GaSb, GaSe, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb,PbO, PbS, PbSe, PbTe, Si, Ge, other Group IV elements, and/or mixturesor alloys thereof, including ternary and quaternary mixtures or alloys.

Examples of the shape of semiconductor nanocrystals include sphere, rod,disk, other shape or mixtures thereof.

Preferably, the semiconductor nanocrystals include a “core” of one ormore first semiconductor materials, which may be surrounded by anovercoating or “shell” of one or more second semiconductor materials. Asemiconductor nanocrystal core surrounded by a semiconductor shell isalso referred to as a “core/shell” semiconductor nanocrystal.

For example, the semiconductor nanocrystal can include a core having theformula MX, where M is cadmium, zinc, magnesium, mercury, aluminum,gallium, indium, thallium, or mixtures thereof, and X is oxygen, sulfur,selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, ormixtures thereof. Examples of materials suitable for use assemiconductor nanocrystal cores include, but are not limited to, CdO,CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, MgO, MgS, MgSe, MgTe, GaAs, GaP,GaSb, GaN, HgO, HgS, HgSe, HgTe, InAs, InP, InSb, InN, AlAs, AlP, AlSb,AlS, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, Ge, Si, other Group IVelements, and/or mixtures or alloys thereof, including ternary andquarternary mixtures or alloys.

The shell can be a semiconductor material having a composition that isthe same as or different from the composition of the core. The shellcomprises an overcoat of a semiconductor material on a surface of thecore semiconductor nanocrystal can include a Group IV element, a GroupII-VI compound, a Group II-V compound, a Group III-VI compound, a GroupIII-V compound, a Group IV-VI compound, a Group I-III-VI compound, aGroup II-IV-VI compound, a Group II-IV-V compound, alloys of any of theforegoing, and/or mixtures of any of the foregoing, including ternaryand quaternary mixtures and/or alloys. Examples include, but are notlimited to, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe,MgTe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP,InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe,Si, Ge, other Group IV elements, and/or mixtures and/or alloys thereof,including ternary and quaternary mixtures and/or alloys. For example,ZnS, ZnSe or CdS overcoatings can be grown on CdSe or CdTe semiconductornanocrystals. An overcoating process is described, for example, in U.S.Pat. No. 6,322,901. By adjusting the temperature of the reaction mixtureduring overcoating and monitoring the absorption spectrum of the core,over coated materials having high emission quantum efficiencies andnarrow size distributions can be obtained. The overcoating may compriseone or more layers. The overcoating comprises at least one semiconductormaterial which is the same as or different from the composition of thecore. Preferably, the overcoating has a thickness of from about one toabout ten monolayers. An overcoating can also have a thickness greaterthan ten monolayers. In certain embodiments, more than one overcoatingcan be included on a core.

In certain embodiments, the surrounding “shell” material can have a bandgap greater than the band gap of the core material. In certainembodiments, the surrounding shell material can have a band gap lessthan the band gap of the core material.

In certain embodiments, the shell can be chosen so as to have an atomicspacing close to that of the “core” substrate. In certain embodiments,the shell and core materials can have the same crystal structure.

Examples of semiconductor nanocrystal (core)shell materials include,without limitation: red (e.g., (CdSe)ZnS (core)shell), green (e.g.,(CdZnSe)CdZnS (core)shell, etc.), and blue (e.g., (CdS)CdZnS(core)shell.

Additional examples of core/shell semiconductor structures are describedin U.S. application Ser. No. 10/638,546, for “Semiconductor NanocrystalHeterostructures”, filed 12 Aug. 2003, and U.S. Published PatentApplication No. US 2004-0023010 A1, for “Light Emitting Device IncludingSemiconductor Nanocrystals” of Bulovic et al. The foregoing applicationsare hereby incorporated herein by reference in its entirety.

Preparation and manipulation of semiconductor nanocrystals aredescribed, for example, in U.S. Pat. Nos. 6,322,901 and 6,576,291, andU.S. Patent Application No. 60/550,314, each of which is herebyincorporated herein by reference in its entirety. One method ofmanufacturing a semiconductor nanocrystal is a colloidal growth process.Colloidal growth occurs by injection an M donor and an X donor into ahot coordinating solvent. One example of a preferred method forpreparing monodisperse semiconductor nanocrystals comprises pyrolysis oforganometallic reagents, such as dimethyl cadmium, injected into a hot,coordinating solvent. This permits discrete nucleation and results inthe controlled growth of macroscopic quantities of semiconductornanocrystals. The injection produces a nucleus that can be grown in acontrolled manner to form a semiconductor nanocrystal. The reactionmixture can be gently heated to grow and anneal the semiconductornanocrystal. Both the average size and the size distribution of thesemiconductor nanocrystals in a sample are dependent on the growthtemperature. The growth temperature necessary to maintain steady growthincreases with increasing average crystal size. The semiconductornanocrystal is a member of a population of semiconductor nanocrystals.As a result of the discrete nucleation and controlled growth, thepopulation of semiconductor nanocrystals that can be obtained has anarrow, monodisperse distribution of diameters. The monodispersedistribution of diameters can also be referred to as a size. Preferably,a monodisperse population of particles includes a population ofparticles wherein at least 60% of the particles in the population fallwithin a specified particle size range. A population of monodisperseparticles preferably deviate less than 15% rms (root-mean-square) indiameter and more preferably less than 10% rms and most preferably lessthan 5%.

In certain embodiments, the preparation of semiconductor nanocrystalscan be carried out in the presence of an amine. See, for example, U.S.Pat. No. 6,576,291 for “Preparation of Nanocrsytallites” of Bawendi etal. issued 10 Jun. 2003, which is hereby incorporated herein byreference in its entirety.

The narrow size distribution of the semiconductor nanocrystals allowsthe possibility of light emission in narrow spectral widths.Monodisperse semiconductor nanocrystals have been described in detail inMurray et al. (J. Am. Chem. Soc., 115:8706 (1993)); in the thesis ofChristopher Murray, “Synthesis and Characterization of 1′-VI QuantumDots and Their Assembly into 3-D Quantum Dot Superlattices”,Massachusetts Institute of Technology, September, 1995; and in U.S.patent application Ser. No. 08/969,302 for “Highly LuminescentColor-Selective Materials”. The foregoing are hereby incorporated hereinby reference in their entireties.

The process of controlled growth and annealing of the semiconductornanocrystals in the coordinating solvent that follows nucleation canalso result in uniform surface derivatization and regular corestructures. As the size distribution sharpens, the temperature can beraised to maintain steady growth. By adding more M donor or X donor, thegrowth period can be shortened. The M donor can be an inorganiccompound, an organometallic compound, or elemental metal. M is cadmium,zinc, magnesium, mercury, aluminum, gallium, indium or thallium. The Xdonor is a compound capable of reacting with the M donor to form amaterial with the general formula MX. The X donor can be a chalcogenidedonor or a pnictide donor, such as a phosphine chalcogenide, abis(silyl) chalcogenide, dioxygen, an ammonium salt, or a tris(silyl)pnictide. Suitable X donors include dioxygen, bis(trimethylsilyl)selenide ((TMS)₂Se), trialkyl phosphine selenides such as(tri-noctylphosphine) selenide (TOPSe) or (tri-n-butylphosphine)selenide (TBPSe), trialkyl phosphine tellurides such as(tri-n-octylphosphine) telluride (TOPTe) or hexapropylphosphorustriamidetelluride (HPPTTe), bis(trimethylsilyl)telluride ((TMS)₂Te),bis(trimethylsilyl)sulfide ((TMS)₂S), a trialkyl phosphine sulfide suchas (tri-noctylphosphine) sulfide (TOPS), an ammonium salt such as anammonium halide (e.g., NH4Cl), tris(trimethylsilyl) phosphide ((TMS)₃P),tris(trimethylsilyl) arsenide ((TMS)₃As), or tris(trimethylsilyl)antimonide ((TMS)₃Sb). In certain embodiments, the M donor and the Xdonor can be moieties within the same molecule.

A coordinating solvent can help control the growth of the semiconductornanocrystal. The coordinating solvent is a compound having a donor lonepair that, for example, has a lone electron pair available to coordinateto a surface of the growing semiconductor nanocrystal. Solventcoordination can stabilize the growing semiconductor nanocrystal.Examples of coordinating solvents include alkyl phosphines, alkylphosphine oxides, alkyl phosphonic acids, or alkyl phosphinic acids,however, other coordinating solvents, such as pyridines, furans, andamines may also be suitable for the semiconductor nanocrystalproduction. Examples of suitable coordinating solvents include pyridine,tri-n-octyl phosphine (TOP), tri-n-octyl phosphine oxide (TOPO) andtrishydroxylpropylphosphine (tHPP). Technical grade TOPO can be used.Non-coordinating solvents can also be used.

Size distribution during the growth stage of the reaction can beestimated by monitoring the absorption or emission line widths of theparticles. Modification of the reaction temperature in response tochanges in the absorption spectrum of the particles allows themaintenance of a sharp particle size distribution during growth.Reactants can be added to the nucleation solution during crystal growthto grow larger crystals. For example, for CdSe and CdTe, by stoppinggrowth at a particular semiconductor nanocrystal average diameter andchoosing the proper composition of the semiconducting material, theemission spectra of the semiconductor nanocrystals can be tunedcontinuously over the wavelength range of 300 nm to 5 microns, or from400 nm to 800 nm n.

The particle size distribution of the semiconductor nanocrystals can befurther refined by size selective precipitation with a poor solvent forthe semiconductor nanocrystals, such as methanol/butanol as described inU.S. Pat. No. 6,322,901. For example, semiconductor nanocrystals can bedispersed in a solution of 10% butanol in hexane. Methanol can be addeddropwise to this stirring solution until opalescence persists.Separation of supernatant and flocculate by centrifugation produces aprecipitate enriched with the largest crystallites in the sample. Thisprocedure can be repeated until no further sharpening of the opticalabsorption spectrum is noted. Size-selective precipitation can becarried out in a variety of solvent/nonsolvent pairs, includingpyridine/hexane and chloroform/methanol. The size-selected semiconductornanocrystal population preferably has no more than a 15% rms deviationfrom mean diameter, more preferably 10% rms deviation or less, and mostpreferably 5% rms deviation or less.

As discussed herein, in certain embodiments, the nanomaterial comprisessemiconductor nanocrystals wherein at least a portion of thesemiconductor nanocrystals include one or more ligands attached to asurface thereof.

In one embodiment, the ligands are derived from the coordinating solventused during the growth process. The surface can be modified by repeatedexposure to an excess of a competing coordinating group to form anoverlayer. For example, a dispersion of the capped semiconductornanocrystal can be treated with a coordinating organic compound, such aspyridine, to produce crystallites which disperse readily in pyridine,methanol, and aromatics but no longer disperse in aliphatic solvents.Such a surface exchange process can be carried out with any compoundcapable of coordinating to or bonding with the outer surface of thesemiconductor nanocrystal, including, for example, phosphines, thiols,amines and phosphates. The semiconductor nanocrystal can be exposed toshort chain polymers which exhibit an affinity for the surface and whichterminate in a moiety having an affinity for a liquid medium in whichthe semiconductor nanocrystal is suspended or dispersed. Such affinityimproves the stability of the suspension and discourages flocculation ofthe semiconductor nanocrystal.

The organic ligands can be useful in facilitating large area,non-epitaxial deposition of highly stable inorganic nanocrystals withina device.

More specifically, the coordinating ligand can have the formula:

(Y—)_(k-n)—(X)-(-L)_(n)

wherein k is 2, 3 or 5, and n is 1, 2, 3, 4 or 5 such that k-n is notless than zero; X is O, S, S═O, SO2, Se, Se═O, N, N═O, P, P═O, As, orAs═O; each of Y and L, independently, is aryl, heteroaryl, or a straightor branched C2-12 hydrocarbon chain optionally containing at least onedouble bond, at least one triple bond, or at least one double bond andone triple bond. The hydrocarbon chain can be optionally substitutedwith one or more C1-4 alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy,hydroxyl, halo, amino, nitro, cyano, C3-5 cycloalkyl, 3-5 memberedheterocycloalkyl, aryl, heteroaryl, C1-4 alkylcarbonyloxy, C1-4alkyloxycarbonyl, C1-4 alkylcarbonyl, or formyl The hydrocarbon chaincan also be optionally interrupted by —O—, —S—, —N(R_(a))—,—N(R_(a))—C(O)—O—, —O—C(O)—N(R_(a))—, —N(R_(a))—C(O)—N(R_(b))—,—O—C(O)—O—, —P(R_(a))—, or —P(O)(R_(a))—. Each of R_(a) and R_(b),independently, is hydrogen, alkyl, alkenyl, alkynyl, alkoxy,hydroxylalkyl, hydroxyl, or haloalkyl. An aryl group is a substituted orunsubstituted cyclic aromatic group. Examples include phenyl, benzyl,naphthyl, tolyl, anthracyl, nitrophenyl, or halophenyl. A heteroarylgroup is an aryl group with one or more heteroatoms in the ring, forinstance furyl, pyridyl, pyrrolyl, phenanthryl.

A suitable coordinating ligand can be purchased commercially or preparedby ordinary synthetic organic techniques, for example, as described inJ. March, Advanced Organic Chemistry, which is hereby incorporated byreference in its entirety.

Other ligands are described in U.S. patent application Ser. No.10/641,292 for “Stabilized Semiconductor Nanocrystals”, filed 15 Aug.2003, which is hereby incorporated herein by reference in its entirety.

When the electron and hole localize on a semiconductor nanocrystal,emission can occur at an emission wavelength. The emission has afrequency that corresponds to the band gap of the quantum confinedsemiconductor material. The band gap is a function of the size of thesemiconductor nanocrystal. Semiconductor nanocrystals having smalldiameters can have properties intermediate between molecular and bulkforms of matter. For example, semiconductor nanocrystals based onsemiconductor materials having small diameters can exhibit quantumconfinement of both the electron and hole in all three dimensions, whichleads to an increase in the effective band gap of the material withdecreasing crystallite size. Consequently, both the optical absorptionand emission of semiconductor nanocrystals shift to the blue, or tohigher energies, as the size of the crystallites decreases.

The emission from a semiconductor nanocrystal can be a narrow Gaussianemission band that can be tuned through the complete wavelength range ofthe ultraviolet, visible, or infra-red regions of the spectrum byvarying the size of the semiconductor nanocrystal, the composition ofthe semiconductor nanocrystal, or both. For example, CdSe can be tunedin the visible region and InAs can be tuned in the infra-red region. Thenarrow size distribution of a population of semiconductor nanocrystalscan result in emission of light in a narrow spectral range. Thepopulation can be monodisperse preferably exhibits less than a 15% rms(root-mean-square) deviation in diameter of the semiconductornanocrystals, more preferably less than 10%, most preferably less than5%. Spectral emissions in a narrow range of no greater than about 75 nm,preferably 60 nm, more preferably 40 nm, and most preferably 30 nm fullwidth at half max (FWHM) for semiconductor nanocrystals that emit in thevisible can be observed. IR-emitting semiconductor nanocrystals can havea FWHM of no greater than 150 nm, or no greater than 100 nm. Expressedin terms of the energy of the emission, the emission can have a FWHM ofno greater than 0.05 eV, or no greater than 0.03 eV. The breadth of theemission decreases as the dispersity of semiconductor nanocrystaldiameters decreases. Semiconductor nanocrystals can have high emissionquantum efficiencies such as greater than 10%, 20%, 30%, 40%, 50%, 60%,70%, or 80%.

The narrow FWHM of semiconductor nanocrystals can result in saturatedcolor emission. This can lead to efficient lighting devices even in thered and blue parts of the visible spectrum, since in semiconductornanocrystal emitting devices no photons are lost to infra-red and UVemission. The broadly tunable, saturated color emission over the entirevisible spectrum of a single material system is unmatched by any classof organic chromophores (see, for example, Dabbousi et al., J. Phys.Chem. 101, 9463 (1997), which is incorporated by reference in itsentirety). A monodisperse population of semiconductor nanocrystals willemit light spanning a narrow range of wavelengths. A device includingsemiconductor nanocrystals of different compositions, sizes, and/orstructures can emit light in more than one narrow range of wavelengths.The color of emitted light perceived by a viewer can be controlled byselecting appropriate combinations of semiconductor nanocrystal sizesand materials in the device as well as relative subpixel currents. Thedegeneracy of the band edge energy levels of semiconductor nanocrystalsfacilitates capture and radiative recombination of all possibleexcitons, whether generated by direct charge injection or energytransfer. The maximum theoretical semiconductor nanocrystal lightingdevice efficiencies are therefore comparable to the unity efficiency ofphosphorescent organic light-emitting devices. The excited statelifetime (τ) of the semiconductor nanocrystal is much shorter (τ˜10 ns)than a typical phosphor (τ>0.1 μs), enabling semiconductor nanocrystallighting devices to operate efficiently even at high current density andhigh brightness.

Transmission electron microscopy (TEM) can provide information about thesize, shape, and distribution of the semiconductor nanocrystalpopulation. Powder X-ray diffraction (XRD) patterns can provide the mostcomplete information regarding the type and quality of the crystalstructure of the semiconductor nanocrystals. Estimates of size are alsopossible since particle diameter is inversely related, via the X-raycoherence length, to the peak width. For example, the diameter of thesemiconductor nanocrystal can be measured directly by transmissionelectron microscopy or estimated from X-ray diffraction data using, forexample, the Scherrer equation. It also can be estimated from the UV/Visabsorption spectrum.

A nanomaterial can be deposited onto a material or device layer inaccordance with the invention. In certain embodiments, the nanomaterialis deposited as one or more separate layers. In certain embodiments offabricating a device, nanomaterial can be disposed between any twolayers of the device. For example, nanomaterial can be disposed betweentwo hole transport layers and/or between two electron transport layers.In either case, each of the charge transport layers may further compriseone or more layers. In another embodiment, nanomaterial comprising canbe deposited as one or more separate emissive layers disposed between ahole transport layer and an electron transport layer. As discussedelsewhere herein, other layers may also be included between the electrontransport layers and the hole transport layers. When included in thedevice as a separate layer, for example, nanomaterial comprisingsemiconductor nanocrystals can be disposed as a continuous orsubstantially continuous thin film or layer. When disposed as a separatelayer, the layer can be patterned or unpatterned. Preferably, thenanomaterial comprising semiconductor nanocrystals included in thedevice comprises a substantially monodisperse population ofsemiconductor nanocrystals.

In certain embodiments, a nanomaterial comprising semiconductornanocrystals and a material capable of transporting charge are depositedfrom the ink at a thickness of multiple monolayers or less. For example,the thickness can be greater than three monolayers, three or lessmonolayers, two or less monolayers, a single monolayer, a partialmonolayer, etc. The thickness of each deposited layer of nanomaterialcomprising semiconductor nanocrystals and material capable oftransporting charge may vary. Preferably, the variation of the thicknessat any point of the deposited material including semiconductornanocrystals and a material capable of transporting charge is less thanthree monolayers, more preferably less than two monolayers, and mostpreferably less than one monolayer. When deposited as a singlemonolayer, preferably at least about 60% of the semiconductornanocrystals are at single monolayer thickness, more preferably, atleast about 80% of the semiconductor nanocrystals are at singlemonolayer thickness, and most preferably, at least about 90% of thesemiconductor nanocrystals are at single monolayer thickness. In alight-emitting device, a monolayer can provide the beneficial lightemission properties of semiconductor nanocrystals while minimizing theimpact on electrical performance. The inclusion of a material capable oftransporting charge in the ink including semiconductor nanocrystals canfurther improve the light emission properties of the semiconductornanocrystals while also having a beneficial affect on electricalperformance

Semiconductor nanocrystals show strong quantum confinement effects thatcan be harnessed in designing bottom-up chemical approaches to createcomplex heterostructures with electronic and optical properties that aretunable with the size and composition of the semiconductor nanocrystals.

As discussed herein, in certain embodiments, nanomaterial comprisingsemiconductor nanocrystals can be deposited in a patterned arrangement.Patterned semiconductor nanocrystals can be used to form an array ofpixels comprising, e.g., red, green, and blue, or alternatively, red,orange, yellow, green, blue-green, blue, violet, or other visible,infrared, or ultraviolet emitting, or other combinations ofdistinguishable wavelength emitting pixels, that are energized toproduce light of a predetermined wavelength.

Generally, a device or array of devices capable of emitting a variety ofcolors includes a pattern of emissive materials capable of emittingdifferent colors. Depositing nanomaterials from inks using inkjetprintheads and/or other micro-dispensers allows such pattern to bedeposited without the use of shadow masks and other patterningtechniques associated with vapor phase deposition. Such depositionprocess also eliminates the need for a transfer step as in contactprinting.

When deposited in a patterned arrangement, features including ananomaterial and a material capable of transporting charge can bedeposited in a pattern including features having at least one dimensionat a micron-scale (e.g., less than 1 mm, less than 500 μm, less than 200μm, less than 100 μm or less, less than 50 μm or less, less than 20 μmor less). Features including a nanomaterial and a material capable oftransporting charge can also be deposited in a patterned arrangementcomprising features at greater than micron-scale.

A pattern comprising features on the micron scale may also be referredto herein as a micropattern. A micropattern can have features on themicron scale, such as less than 1 mm, less than 500 μm, less than 200μm, less than 100 μm, less than 50 μm, or 20 μm or less in size. A 20 μmfeature size is sufficiently small for most light emitting devices anddevices for other applications.

The surface on which ink comprising a nanomaterial, a material capableof transporting charge, and a liquid vehicle can be deposited can havedimensions of 1 cm or greater, 10 cm or greater, 100 cm or greater, or1,000 cm or greater.

Methods in accordance with the invention are scalable and can be usefulin depositing a pattern comprising one or more nanomaterials over a widerange of surface areas.

For example, the method is useful for depositing nanomaterial over verysmall areas (for example, 100 μm catheters) to very large areas, (forexample, 12″ square areas). In further example, the method is alsouseful for depositing nanomaterial over surfaces with dimensions such asGEN2 (360 mm×465 mm), GEN3 (550 mm×650 mm), GEN3.5 (600 mm×720 mm), GEN4(730 mm×920 mm), GEN5 (1110 mm×1250 mm), GEN6 (1500 mm×1800 mm), GEN7(1900 mm×2100 mm), and subsequent generations of glass that can be used,e.g., in displays. Optionally, areas onto which nanomaterial is appliedcan then be stitched (or tiled) together, to expand the printable areafrom 12″ squares, to ‘n×12″ squares’ as is frequently done in thesemiconductor lithography field.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix.

An example of an embodiment of a light-emitting device is shown in FIG.2. The depicted example includes a first electrode disposed over asubstrate, a first layer in electrical connection with the firstelectrode, a second layer in electrical connection with the first layer,and a second electrode in electrical connection with the second layer.The first layer can comprise a material capable of transporting holes(HTL) and the second layer can comprise a material capable oftransporting electrons (ETL). At least one layer can be non-polymeric.An emissive material is included between the two electrodes. An emissivematerial is included between the two electrodes. The emissive materialcan include a plurality of semiconductor nanocrystals that can beselected based upon their light-emissive characteristics (e.g., thewavelength of the photon emitted by the nanocrystal when voltage isapplied across the device). The emissive material can be included as one(as shown in FIG. 2) or more layers between the first layer and thesecond layer. In the figures the layer including the emissive materialis designated as a “quantum dot layer”. In certain embodiments, a layerincluding the emissive material can include semiconductor nanocrystalsat a thickness of approximately a monolayer. In other embodiments, alayer including an emissive material comprising a plurality ofsemiconductor nanocrystals can include semiconductor nanocrystals at athickness of three monolayers or less or at a thickness of greater thanthree monolayers. In the embodiment depicted in FIG. 2 the firstelectrode of the structure is in contact with the substrate. Eachelectrode can be connected to a power supply to provide a voltage acrossthe structure. Electroluminescence can be produced by the semiconductornanocrystals included in the device when a voltage of proper polarity isapplied across the heterostructure.

The device structure depicted in FIG. 2 maybe fabricated as follows. Asubstrate having a first electrode (e.g., an anode) disposed thereon maybe obtained or fabricated using any suitable technique. The firstelectrode may be patterned. A first layer (e.g., a hole transport layer)may be deposited using any suitable technique. An emissive layer isdeposited from an ink including a nanomaterial comprising semiconductornanocrystals, a material capable of transporting charge, and a liquidvehicle from a micro-dispenser, e.g., inkjet printhead. Inkjet printingis preferred, because it readily allows for the patterning of separateregions. In certain embodiments, the liquid vehicle of the ink isselected such that, upon removal of the liquid vehicle, the layer(s) ofthe device are planar (for example, utilizing a well structure such astypically used in polymer light emitting device (PLED) technology). Asecond layer (e.g., an electron transport layer) may be deposited usingany suitable technique. A second electrode (e.g., a cathode) may bedeposited using any suitable technique.

In the example shown in FIG. 2, light is emitted from the bottom of thestructure (through, e.g., ITO coated glass). If an adequately lighttransmissive top electrode is used, the structure could emit light fromthe top of the structure.

Alternatively, the structure of FIG. 2 can be inverted, in which caselight can be emitted from the top.

The simple layered structure illustrated in FIG. 2 is provided by way ofnon-limiting example, and it is understood that embodiments of theinvention may be used in connection with a wide variety of otherstructures. The specific materials and structures described herein areexemplary in nature, and other materials and structures may be used.Functional devices may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be limiting.

The color of the light output of a light-emitting device can beprecisely controlled by the selection of the composition, structure, andsize of the various semiconductor nanocrystals included in a device asthe emissive material. In certain embodiments, two or more differentsemiconductor nanocrystals (having different compositions, structures,and/or sizes) can be included.

FIG. 3 illustrates an example of another embodiment of a light-emittingdevice showing a glass substrate on which the device can be built and aprotective glass layer that can be used to encapsulate the device.

Optionally a desiccant or other moisture absorptive material can beincluded in the device before it is sealed, e.g., with an epoxy, such asa UV curable expoxy. Other desiccants or moisture absorptive materialscan be used.

The first electrode can be, for example, an anode comprising a high workfunction (e.g., great than 4.0 eV) hole-injecting conductor, such as anindium tin oxide (ITO) layer. Other anode materials include other highwork function hole-injection conductors including, but not limited to,for example, tungsten, nickel, cobalt, platinum, palladium and theiralloys, gallium indium tin oxide, zinc indium tin oxide, titaniumnitride, polyaniline, or other high work function hole-injectionconducting polymers. In certain embodiments, the first electrode islight transmissive or transparent. In addition to ITO, examples of otherlight-transmissive electrode materials include conducting polymers, andother metal oxides, low or high work function metals, or conductingepoxy resins that are at least partially light transmissive. An exampleof a conducting polymer that can be used as an electrode material ispoly(ethlyendioxythiophene), sold by Bayer AG under the trade markPEDOT. Other molecularly altered poly(thiophenes) are also conductingand could be used, as well as emaraldine salt form of polyaniline.

The second electrode can be, for example, a cathode comprising a lowwork function (e.g., less than 4.0 eV), electron-injecting, metal, suchas Al, Ba, Yb, Ca, a lithium-aluminum alloy (Li:Al), a magnesium-silveralloy (Mg:Ag), or lithium fluoride-aluminum (LiF:Al). The secondelectrode, such as Mg:Ag, can optionally be covered with an opaqueprotective metal layer, for example, a layer of Ag for protecting thecathode layer from atmospheric oxidation, or a relatively thin layer ofsubstantially transparent ITO. The second electrode can be sandwiched,sputtered, or evaporated onto the exposed surface of the solid layer.One or both of the electrodes can be patterned. The electrodes of thedevice can be connected to a voltage source by electrically conductivepathways. Upon application of the voltage, light is generated from thedevice.

In a device such as that shown in FIG. 2, for example, the firstelectrode can have a thickness of about 500 Angstroms to 4000 Angstroms.The first layer can have a thickness of about 50 Angstroms to about 1000Angstroms. The second layer can have a thickness of about 50 Angstromsto about 1000 Angstroms. The second electrode can have a thickness ofabout 50 Angstroms to greater than about 1000 Angstroms.

Non-polymeric electrode materials can be deposited by, for example,sputtering or evaporating. Polymeric electrode materials can bedeposited by, for example, spin-casting.

As discussed above, the electrodes can be patterned. Electrode material,including light-transmittable electrode material, can be patterned by,for example, a chemical etching method such as a photolithography or aphysical etching method using laser, etc. Also, the electrode may bepatterned by vacuum vapor deposition, sputtering, etc. while masking.

Hole transport and electron transport layers can be collectivelyreferred to as charge transport layers. Either or both of these layerscan comprise organic or inorganic materials. Examples of inorganicmaterial include, for example, inorganic semiconductors. The inorganicmaterial can be amorphous or polycrystalline. An organic chargetransport material can be polymeric or non-polymeric.

An example of a typical organic material that can be included in anelectron transport layer includes a molecular matrix. The molecularmatrix can be non-polymeric. The molecular matrix can include a smallmolecule, for example, a metal complex. The metal complex of8-hydroxyquinoline can be an aluminum, gallium, indium, zinc ormagnesium complex, for example, aluminum tris(8-hydroxyquinoline)(Alq₃). Other classes of materials in the electron transport layer caninclude metal thioxinoid compounds, oxadiazole metal chelates,triazoles, sexithiophenes derivatives, pyrazine, and styrylanthracenederivatives. Balq2 is an example of another material that can beincluded in an electron transport layer. An electron transport layercomprising an organic material may be intrinsic (undoped) or doped.Doping may be used to enhance conductivity. See, for example, U.S.Provisional Patent Application No. 60/795,420 of Beatty et al, for“Device Including Semiconductor Nanocrystals And A Layer Including ADoped Organic Material And Methods”, filed 27 Apr. 2006, which is herebyincorporated herein by reference in its entirety.

An example of a typical organic material that can be included in a holetransport layer includes an organic chromophore. The organic chromophorecan include a phenyl amine, such as, for example,N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TPD). Other hole transport layer can includeN,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)-spiro (spiro-TPD),4-4′-N,N′-dicarbazolyl-biphenyl (CBP),4,4-.bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD), etc., apolyaniline, a polypyrrole, a poly(phenylene vinylene), copperphthalocyanine, an aromatic tertiary amine or polynuclear aromatictertiary amine, a 4,4′-bis(p-carbazolyl)-1,1′-biphenyl compound, or anN,N,N′,N′-tetraarylbenzidine. A hole transport layer comprising anorganic material may be intrinsic (undoped) or doped. Doping may be usedto enhance conductivity. Examples of doped hole transport layers aredescribed in U.S. Provisional Patent Application No. 60/795,420 ofBeatty et al, for “Device Including Semiconductor Nanocrystals And ALayer Including A Doped Organic Material And Methods”, filed 27 Apr.2006, which is hereby incorporated herein by reference in its entirety.

Charge transport layers comprising organic materials and otherinformation related to fabrication of organic charge transport layers,light-emitting devices, and related technology are discussed in moredetail in U.S. patent application Ser. No. 11/253,612 for “Method AndSystem For Transferring A Patterned Material”, filed 21 Oct. 2005, andSer. No. 11/253,595 for “Light Emitting Device Including SemiconductorNanocrystals”, filed 21 Oct. 2005 and International Patent ApplicationNo. PCT/US2007/13152 for “Light-Emitting Devices And Displays WithImproved Performance”, filed 4 Jun. 2007. The foregoing patentapplications are hereby incorporated herein by reference in itsentirety.

Organic charge transport layers may be disposed by known methods such asa vacuum vapor deposition method, a sputtering method, a dip-coatingmethod, a spin-coating method, a casting method, a bar-coating method, aroll-coating method, and other film deposition methods. In certainembodiments, organic layers are deposited under ultra-high vacuum (e.g.,<1-8 torr), high vacuum (e.g., from about 10⁻⁸ torr to about 10⁻⁵ torr),or low vacuum conditions (e.g., from about 10⁻⁵ torr to about 10⁻³torr). Preferably, the organic layers are deposited at high vacuumconditions of from about 1×10⁻⁷ to about 1×10⁻⁶ torr or from about1×10⁻⁷ to about 5×10⁻⁶ torr. Alternatively, organic layers may be formedby multi-layer coating while appropriately selecting solvent for eachlayer.

Charge transport layers including inorganic materials and otherinformation related to fabrication of inorganic charge transport layersare discussed further below and in more detail in U.S. PatentApplication No. 60/653,094 for “Light Emitting Device IncludingSemiconductor Nanocrystals, filed 16 Feb. 2005 and U.S. patentapplication Ser. No. 11/354,185, filed 15 Feb. 2006, the disclosures ofeach of which are hereby incorporated herein by reference in theirentireties.

Charge transport layers comprising an inorganic semiconductor can bedeposited on a substrate at a low temperature, for example, by a knownmethod, such as a vacuum vapor deposition method, an ion-plating method,sputtering, inkjet printing, etc.

The substrate can be opaque, light transmissive, or transparent. Thesubstrate can be rigid or flexible. The substrate can be plastic, metalor glass.

In some applications, the substrate can include a backplane. Thebackplane includes active or passive electronics for controlling orswitching power to individual pixels. Including a backplane can beuseful for applications such as displays, sensors, or imagers. Inparticular, the backplane can be configured as an active matrix, passivematrix, fixed format, direct drive, or hybrid. The display can beconfigured for still images, moving images, or lighting. A displayincluding an array of light emitting devices can provide white light,monochrome light, or color-tunable light.

In addition to the charge transport layers, a device may optionallyfurther include one or more charge-injection layers, e.g., ahole-injection layer (either as a separate layer or as part of the holetransport layer) and/or an electron-injection layer (either as aseparate layer as part of the electron transport layer). Chargeinjection layers comprising organic materials can be intrinsic(un-doped) or doped. See, for example, U.S. Provisional PatentApplication No. 60/795,420 of Beatty et al, for “Device IncludingSemiconductor Nanocrystals And A Layer Including A Doped OrganicMaterial And Methods”, filed 27 Apr. 2006, which is hereby incorporatedherein by reference in its entirety.

One or more charge blocking layers may still further optionally beincluded. For example, an electron blocking layer (EBL), a hole blockinglayer (HBL), or an exciton blocking layer (eBL), can be introduced inthe structure. A blocking layer can include, for example,3-(4-biphenylyl)-4-phenyl-5-tert butylphenyl-1,2,4-triazole (TAZ),2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TBPi),3,4,5-triphenyl-1,2,4-triazole,3,5-bis(4-tert-butylphenyl)-4-phenyl-1,2,4-triazole, bathocuproine(BCP), 4,4′,4″-tris{N-(3-methylphenyl)-Nphenylamino}triphenylamine(m-MTDATA), polyethylene dioxythiophene (PEDOT),1,3-bis(5-(4-diphenylamino)phenyl-1,3,4-oxadiazol-2-yl)benzene,2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,3,4-oxadiazole,1,3-bis[5-(4-(1,1-dimethylethyl)phenyl)-1,3,4-oxadiazol-5,2-yl)benzene,1,4-bis(5-(4-diphenylamino)phenyl-1,3,4-oxadiazol-2-yl)benzene, or1,3,5-tris[5-(4-(1,1-dimethylethyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene.Charge blocking layers comprising organic materials can be intrinsic(un-doped) or doped. See, for example, U.S. Provisional PatentApplication No. 60/795,420 of Beatty et al, for “Device IncludingSemiconductor Nanocrystals And A Layer Including A Doped OrganicMaterial And Methods”, filed 27 Apr. 2006, which is hereby incorporatedherein by reference in its entirety.

The charge injection layers and/or the charge blocking layers, ifincluded, can be deposited on a surface of one of the electrodes by spincoating, dip coating, vapor deposition, or other thin film depositionmethods. See, for example, M. C. Schlamp, et al., J. Appl. Phys., 82,5837-5842, (1997); V. Santhanam, et al., Langmuir, 19, 7881-7887,(2003); and X. Lin, et al., J. Phys. Chem. B, 105, 3353-3357, (2001),each of which is incorporated by reference in its entirety.

Other multilayer structures may optionally be used to improve theperformance (see, for example, U.S. patent application Ser. Nos.10/400,907 and 10/400,908, filed Mar. 28, 2003, each of which isincorporated by reference in its entirety) of the light-emitting devicesand displays of the invention. The performance of light-emitting devicescan be improved by increasing their efficiency, narrowing or broadeningtheir emission spectra, or polarizing their emission. See, for example,Bulovic et al., Semiconductors and Semimetals 64, 255 (2000), Adachi etal., Appl. Phys. Lett. 78, 1622 (2001), Yamasaki et al., Appl. Phys.Lett. 76, 1243 (2000), Dirr et al., Jpn. J. Appl. Phys. 37, 1457 (1998),and D'Andrade et al., MRS Fall Meeting, BB6.2 (2001), each of which isincorporated herein by reference in its entirety.

Preferably, a device including a nanomaterial comprising semiconductornanocrystals is processed in a controlled (oxygen-free andmoisture-free) environment, preventing the quenching of luminescentefficiency during the fabrication process.

Besides being useful to deposit an ink comprising a nanomaterial, amaterial capable of transporting charge, and a liquid vehicle infabricating devices and displays, other layers of a device and/or array(e.g., electrodes, charge transport layers, charge blocking layers,charge injection layers, etc.) can also be deposited frommicro-dispensers, e.g., inkjet printheads. Fabricating multiple devicelayers using micro-dispensers, e.g., inkjet printheads, can simplify themanufacturing process and provide other manufacturing efficiencies.

Because of the diversity of semiconductor nanocrystal materials that canbe prepared, and the wavelength tuning via semiconductor nanocrystalcomposition, structure, and size, devices that can emit light of apredetermined color are possible with use of semiconductor nanocrystalsas the emissive material. Semiconductor nanocrystal light-emitteddevices can be tuned to emit anywhere in the spectrum. Light-emittingdevices can be prepared that emit visible or invisible (e.g., IR) light.The size and material of a semiconductor nanocrystal can be selectedsuch that the semiconductor nanocrystal emits light having apredetermined wavelength. Light emission can be of a predeterminedwavelength in any region of the spectrum, e.g., visible, infrared, etc.For example, the wavelength can be between 300 and 2,500 nm or greater,for instance between 300 and 400 nm, between 400 and 700 nm, between 700and 1100 nm, between 1100 and 2500 nm, or greater than 2500 nm.

In certain embodiments, individual light-emitting devices can be formed.In other embodiments, a plurality of individual light-emitting devicescan be formed at multiple locations on a single substrate to form adisplay.

A display can include two or more devices that emit at the same ordifferent wavelengths. By patterning the substrate with arrays offeatures including nanomaterials comprising different color-emittingsemiconductor nanocrystals and material capable of transporting charge,a display including pixels of different colors can be formed. Patternedfeatures including semiconductor nanocrystals can be used to form anarray of pixels comprising, e.g., red, green, and blue or alternatively,red, yellow, green, blue-green, and/or blue emitting, or othercombinations of distinguishable color emitting subpixels, that areenergized to produce light of a predetermined wavelength.

An individual light-emitting device or one or more light-emittingdevices of a display can optionally include a mixture of differentcolor-emitting semiconductor nanocrystals formulated to produce a whitelight. White light can alternatively be produced from a device includingred, green, blue, and, optionally, additional pixels.

Examples of other displays are included in U.S. Patent Application No.60/771,643 for “Displays Including Semiconductor Nanocrystals AndMethods Of Making Same”, of Seth Coe-Sullivan et al., filed 9 Feb. 2006,the disclosure of which is hereby incorporated herein by reference inits entirety.

As discussed above, the methods described herein may have applicationsin fabricating other devices in addition to light-emitting devices,including, but not limited to, solar cells, photovoltaic devices,photodetectors, non-volatile memory devices, etc.

For example, a nanomaterial, e.g., a nanomaterial comprisingsemiconductor nanocrystals, can be deposited by a method in accordancewith the invention in fabrication of a photodetector device or array ofphotodetector devices. A photodetector device includes one or morenanomaterials comprising a plurality of semiconductor nanocrystals whichare selected based upon absorption properties. When included in aphotodetector, semiconductor nanocrystals are engineered to produce apredetermined electrical response upon absorption of a particularwavelength, typically in the IR or MIR region of the spectrum. Examplesof photodetector devices including semiconductor nanocrystals aredescribed in “A Quantum Dot Heterojunction Photodetector” by AlexiCosmos Arango, Submitted to the Department of Electrical Engineering andComputer Science, in partial fulfillment of the requirements for thedegree of Masters of Science in Computer Science and Engineering at theMassachusetts Institute of Technology, February 2005, the disclosure ofwhich is hereby incorporated herein by reference in its entirety. One ormore photodetectors can further be included in an imaging device, suchas an hyperspectral imaging device. See, for example, U.S. ProvisionalApplication No. 60/785,786 of Coe-Sullivan et al. for “HyperspectralImaging Device”, filed 24 Mar. 2006, the disclosure of which is herebyincorporated herein by reference in its entirety.

In one embodiment, a method of fabricating photodetector device includesdepositing an ink comprising a nanomaterial, a material capable oftransporting charge, and a liquid vehicle onto a layer of the devicefrom a micro-dispenser. In one embodiment, the nanomaterial comprisessemiconductor nanocrystals. The ink can be deposited onto the layer ofthe device in a predetermined patterned arrangement or as an unpatternedarrangement, including, only by way of example, a layer, a continuousfilm, etc. Preferably the liquid vehicle is removed from the depositedink before deposition of any other material or layer thereover.

In another embodiment, a method of fabricating an array of photodetectordevices includes depositing an ink comprising a nanomaterial, a materialcapable of transporting charge, and a liquid vehicle onto a layer of thedevice from a micro-dispenser. In one embodiment, the nanomaterialcomprises semiconductor nanocrystals. The ink comprising a nanomaterial,a material capable of transporting charge, and a liquid vehicle can bedeposited on the device layer in a predetermined patterned arrangement.For example, the ink can be deposited in a patterned or unpatternedarrangement.

The device layer can be disposed on a substrate that further includes anelectrode. A second electrode can be deposited over the depositednanomaterial and material capable of transporting charge, preferablyafter removal of the liquid vehicle from the ink. In one embodiment, thedevice layer onto which the nanomaterial is deposited comprises a chargetransport material. Optionally, a second charge transport layer can beformed between the nanomaterial layer and the second electrode.

A method of fabricating a photodetector device or array of devices canoptionally include depositing one or more nanomaterials in apredetermined arrangement (patterned or unpatterned). As discussedabove, an ink including a nanomaterial, a material capable oftransporting charge, and a liquid vehicle is deposited from amicro-dispenser.

Methods in accordance with the invention can also be used in depositionnanomaterials in the fabrication of memory devices. An example of anonvolatile device is described in U.S. patent application Ser. No.10/958,659, for “Non-Volatile Memory Device”, of Bawendi et al., filed 6Oct. 2004, the disclosure of which is hereby incorporated herein byreference in its entirety.

For additional information relating to semiconductor nanocrystals andtheir use, see also U.S. Patent Application No. 60/620,967, filed Oct.22, 2004, and Ser. No. 11/032,163, filed Jan. 11, 2005, U.S. patentapplication Ser. No. 11/071,244, filed 4 Mar. 2005. Each of theforegoing patent applications is hereby incorporated herein by referencein its entirety.

As used herein, “top” and “bottom” are relative positional terms, basedupon a location from a reference point. More particularly, “top” meansfurthest away from the substrate, while “bottom” means closest to thesubstrate. For example, for a light-emitting device that optionallyincludes two electrodes, the bottom electrode is the electrode closestto the substrate, and is generally the first electrode fabricated; thetop electrode is the electrode that is more remote from the substrate,on the top side of the light-emitting material. The bottom electrode hastwo surfaces, a bottom surface closest to the substrate, and a topsurface further away from the substrate. Where, e.g., a first layer isdescribed as disposed or deposited “over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is otherwise specified.For example, a cathode may be described as “disposed over” an anode,even though there are various organic and/or inorganic layers inbetween.

As used herein, the singular forms “a”, “an” and “the” include pluralunless the context clearly dictates otherwise. Thus, for example,reference to a nanomaterial includes reference to one or more of suchmaterials.

All the patents and publications mentioned above and throughout areincorporated in their entirety by reference herein. Further, when anamount, concentration, or other value or parameter is given as either arange, preferred range, or a list of upper preferable values and lowerpreferable values, this is to be understood as specifically disclosingall ranges formed from any pair of any upper range limit or preferredvalue and any lower range limit or preferred value, regardless ofwhether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1. A method of depositing an emissive material including a nanomaterialcomprising semiconductor nanocrystals that emit light having apredetermined wavelength and a material capable of transporting chargeonto a layer of a light-emitting device, the method comprising:depositing an ink comprising the nanomaterial, the material capable oftransporting charge, and a liquid vehicle from a micro-dispenser onto alayer of a device in a predetermined arrangement, wherein the layer of adevice comprises a material.
 2. A method in accordance with claim 1wherein the liquid vehicle comprises a liquid in which the materialincluded in the layer of a device is insoluble.
 3. A method inaccordance with claim 1 wherein the liquid vehicle comprises a liquid inwhich the material included in the layer of a device is at leastpartially soluble.
 4. A method in accordance with claim 3 wherein atleast a portion of the nanomaterial and the material is at leasttemporarily mixed in a portion of the second material capable oftransporting charge that dissolves in the ink.
 5. A method in accordancewith claim 1 further comprising removing at least a portion of theliquid vehicle from the ink.
 6. A method in accordance with claim 4wherein at least a portion of the liquid vehicle is removed such that atleast a portion of the material remains mixed with the nanomaterial andmaterial capable of transporting charge.
 7. A method in accordance withclaim 5 wherein the liquid vehicle is removed such that the nanomaterialphase separates to form a layer of nanomaterial at or near the surfaceof the material.
 8. A method in accordance with claim 5 wherein theliquid vehicle is selected such that, upon removal of the liquidvehicle, the surface of the material is planar.
 9. A method inaccordance with claim 1 wherein the material comprises a second materialcapable of transporting charge.
 10. A method in accordance with claim 9wherein the second material capable of transporting charge comprises asmall molecule material.
 11. A method in accordance with claim 10wherein the second material capable of transporting charge comprises apolymer.
 12. A method in accordance with claim 10 wherein the secondmaterial capable of transporting charge comprises an inorganic material.13. A method in accordance with claim 9 wherein the second materialcapable of transporting charge comprises a material capable oftransporting electrons.
 14. A method in accordance with claim 9 whereinthe second material capable of transporting charge comprises a materialcapable of transporting holes.
 15. A method in accordance with claim 1wherein the material capable of transporting charge has a triplet energywhich is at least greater than the bandgap of the semiconductornanocrystals included in the ink.
 16. A method in accordance with claim1 wherein the layer of a device is disposed over a substrate. 17.(canceled)
 18. A method in accordance with claim 1 wherein themicro-dispenser comprises an inkjet printhead and the ink is depositedby inkjet processing.
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 26. A method inaccordance with claim 1 wherein more than one ink is deposited onto thelayer, wherein each ink comprises a nanomaterial comprisingsemiconductor nanocrystals.
 27. A method in accordance with claim 26wherein the each ink comprises a nanomaterial comprising semiconductornanocrystals that have an emission wavelength distinguishable from theemission wavelength of the semiconductor nanocrystals included in eachof the other inks.
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 109. (canceled)
 110. (canceled)
 111. An inkcomposition comprising a nanomaterial comprising semiconductornanocrystals, a material capable of transporting charge, and a liquidvehicle, wherein the material capable of transporting charge has atriplet energy which is at least greater than the bandgap of thesemiconductor nanocrystals included in the ink.
 112. (canceled) 113.(canceled)
 114. (canceled)